THE EFFECT OF HABITAT FRAGMENTATION ON THE SPATIAL POPULATION GENETIC STRUCTURE OF SOUTHERN PINE BEETLE (DENDROCTONUS FRONTALIS)

Author

Solomon Ghebremeskel Hailu, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2011

Degree Name

Master of Science

Department

Zoology

First Advisor

Ibrahim, Kamal

Abstract

Southern pine beetle (SPB), Dendroctonus frontalis (Zimmerman), is one of the most destructive insect pests of pine trees in southern United States, Mexico and Central America. There is relatively little information on the effect of habitat fragmentation on the connectivity and the spatial population genetics of SPB. This study therefore, adds to previously generated information by assessing how habitat fragmentation affects the spatial population genetic structure of SPB. It also introduces a new approach to the study of bark beetle population dynamics by assessing how landscape variables shape their effective dispersal. To address this issue, a suite of eight highly polymorphic DNA microsatellite markers were used to measure SPB movement over a representative range of SPB habitat and non-habitat (matrix). At the broadest scale, highly significant genetic differentiation suggests that the sampled populations are not panmictic. Loci with higher variability yielded higher resolution for both the infinite allele model based measure of differentiation (FST) and the stepwise mutation based measure (RST) estimates. It is apparent that allelic frequency differences, allelic size ranges and repeat motif played a role in the observed patterns of pair-wise differentiations between the sampled localities. It is supposed that gene flow, wide-range dispersal and recent divergent time could have contributed to the lower level of genetic structure observed in the pair wise estimates. The sampled populations did not show any differentiation attributable to the host species from which they were collected. Mantel test of genetic distance and Euclidean geographic distance revealed no correlation. Mantel tests of the correlation between genetic distance and cost weighted Euclidean distances also suggest that dispersal of SPB across geographic barriers is not significantly reduced. Thus, landscape features and host preference do not appear to have had an impact on population genetic structure of SPB. Since movements of these beetles were not significantly hindered by environmental factors like major rivers, roads, elevation and host type, it is advisable for regional pest management offices to put an effort and coordinate their prevention and management plans in a broader scale to alleviate the problem associated with this native insect pest. Disequilibrium in the observed homogenized pattern of the beetle in this study suggests human contribution in the dispersal of SPB. Therefore, stringent control is deemed necessary in transportation of logs. This could improve our pest management system hence its positive implication in timber industry is obvious.